I doubt they are failing at spam, at least not in the common sense. My gmail account received 1000's of spam emails a week, and it's a rare for one to pass the

I doubt they are failing at spam, at least not in the common sense. My gmail account received 1000's of spam emails a week, and it's a rare for one to pass the filter, and even rarer for a genuine email to not. It most likely a much simpler explanation: web results with content explicitly generated for a specific target search string is simply getting closer and closer to being actual genuine content, and thus harder and harder to differentiate and filter.